My query looks like this:

SELECT td.therapistId, td.tdId, td.dYear, s.school, d.degree

FROM TherapistDegree AS td, Degree AS d, School AS s

WHERE td.schoolId = s.schoolId AND td.degreeId = d.degreeId AND td.therapistId IN( $tIds )

ORDER BY dYear DESC, degree ASC

Everything works fine except for those pesky therapists who only enter their degree and no school. without a school Id in TherapistDegree, no degree will display at all, even if it is there. How can I modify this query to allow users to leave td.schoolId blank and still see their degree?